Ischemic preconditioning (IPC) in the brain is a robust neuroprotective phenomenon in which a brief ischemic exposure increases resistance to the injurious effects of subsequent prolonged ischemia. Characterizing the cellular and molecular mechanisms of IPC is an active area of investigation in stroke research. Microglia, the brain's specialized tissue macrophages, play a major role in the neuroinflammatory response and in many neurological diseases including stroke. Several lines of evidence support a role for microglia in IPC. Microglia express Toll-like receptors (TLRs) that mediate powerful immune responses to exogenous and endogenous agonists. TLR4 is required for IPC-induced neuroprotection. In order to elucidate the mechanisms by which microglial TLR4 contributes to IPC, we carried out cell-targeted genomic analyses specifically on microglia exposed to either ischemic conditions in vitro or IPC in vivo. Results from both datasets identified robust expression of type 1 and/or type 3 interferon (IFN)-stimulated genes (ISGs) as the predominant transcriptomal feature of ischemia-exposed WT, but not TLR4-/-, microglia. The IFN family of cytokines is recognized as a key component of the innate immune response to infection. Recent work has implicated microglial IFN signaling as an important regulator of the injury response induced by non-infectious mechanisms. The focus of this proposal is to characterize the role of type 1 & 3 IFNs in mediating the IPC phenomenon and the microglial response to ischemia using both in vitro (hypoxia/hypoglycemia treatment of primary microglia) and in vivo (middle cerebral artery occlusion/reperfusion) experimental models.